. The practical telephone handbook and guide to the telephonic exchange . ds are threaded, in two rows, the attachedplugs resting in recesses when not in plugs in the back row are the answer-ing plugs, and those in the front row the calling plugs. Key Shelf.—On the Key Shelf, below theindicator panels, a corresponding number ofcombined listening and ringing keys are ar-ranged in line with the plugs and cords, both sets beingcorrespondingly numbered as a guide. The conductorsof the cords are soldered to tabs, which are clamped tospring cord fasteners fixed on a shelf at the back of theb
. The practical telephone handbook and guide to the telephonic exchange . ds are threaded, in two rows, the attachedplugs resting in recesses when not in plugs in the back row are the answer-ing plugs, and those in the front row the calling plugs. Key Shelf.—On the Key Shelf, below theindicator panels, a corresponding number ofcombined listening and ringing keys are ar-ranged in line with the plugs and cords, both sets beingcorrespondingly numbered as a guide. The conductorsof the cords are soldered to tabs, which are clamped tospring cord fasteners fixed on a shelf at the back of theboard. (A view of one of these fasteners in part section isshown in Fig. 211.) Each of the cords is drawn straight, andkept taut by a brass pulley, to which is attached a lead cords and plugs used on boards on which 5-pointsubscribers jacks are used, need only be of 2-way type, butgenerally 3-way cords and plugs are used, so as to enable theboards to be joined up for multiple working when there arefour or more in one centre. If 7-point jacks are used in the. Fig. 211.—Scale EXCHANGE SWITCH-BOARDS 185 board, 2-way plugs and cords only are needed. For possiblefuture multiple working of the boards it is also usual toemploy an operators set which is differentially wound, andwhich has the centre point of the receiver connected to earth(as shown at R of Fig. 210), to provide an engaged test, asexplained in the next chapter. Operation.—On the sub-station ringing, the drop d isactuated. The operator inserts answering plug into the jack,and presses listening key, so that the round wedge forcesout the long left-hand springs, and thus connects her telephoneset to the calling line. On ascertaining the number wanted,she inserts the calling plug into the jack of that number, andturns her key to the ringing position for a few ringing vibrator shows if current is passing from thegenerator. Ring-Bach Key.—In case it should be necessary to ring the calling subscribe
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelephone, bookyear19
